Image Formation by Spherical Lenses
Define the principal focus of a concave and convex lens.
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Find the position of the image.
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image ?
If an object is placed at the focus of a convex lens, where is the image formed ?
I want some trick to learn the Ray diagrams and solve the problems on it
For the object placed between the optical centre and focus of a convex lens, the image is :
(a) real and enlarged
(b) real and diminished
(c) virtual and enlarged
(d) virtual and diminished.
(a) With the help of a labelled diagram, explain how a concave lens diverges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the concave lens on the diagram. (b) State whether concave lens has a real focus or a virtual focus. (c) List some things that concave lens and convex mirror have in common.
What is the nature of the image formed by a convex lens if the magnification produced by the lens is +3 ?
(a) An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is (i) converging, and (ii) diverging. (b) State one practical use each of convex mirror, concave mirror, convex lens and concave lens.
Draw a ray diagram to show how a converging lens is used as a magnifying glass to observe a small object. Mark on your diagram the foci of the lens and the position of the eye.
(a) Explain what is meant by a virtual, magnified image. (b) Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly. (c) Three convex lenses are available having focal lengths of 4 cm, 40 cm and 4 m respectively. Which one would you choose as a magnifying glass and why ?
For an object placed at a distance 20 cm in front of a convex lens, the image is at a distance 20 cm behind the lens. The focal length of convex lens is :
(a) 20 cm (b) 10 cm (c) 15 cm (d) 40 cm
When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object. (a) What is the focal length of lens A ? (b) What is the focal length of lens B ? (c) What is the nature of lens A ? (d) What is the nature of lens B ?
When an object is kept at any distance in front of a concave lens, the image formed is always : (a) virtual, erect and magnified (b) virtual, inverted and diminished. (c) virtual, erect and diminished (d) virtual, erect and same size as object
A convex lens has a focal length of 10 cm. At which of the following position should an object be placed so that this convex lens may act as a magnifying glass ? (a) 15 cm (b) 7 cm (c) 20 cm (d) 25 cm
An object is placed at a distance equal to 2f in front of a convex lens. Draw a labelled ray diagram to show the formation of image. State two characteristics of the image formed.
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens ? Draw the ray-diagram.
When an object is placed at a distance of 36 cm from a convex lens, an image of the same size as the object is formed. What will be the nature of image formed when the object is placed at a distance of :
(a) 10 cm from the lens ?
(b) 20 cm from the lens ?
An object is placed between f and 2f of a convex lens. Which of the following statements correctly describes its image ? (a) real, larger than the object (c) inverted, same size as object
A virtual, erect and magnified image of an object is to be obtained with a convex lens. For this purpose, the object should be placed : (a) between 2F and infinity (b) between F and optical centre (c) between F and 2F (d) at F
Why can a normal person see distant as well as nearby objects clearly?
An illuminated object is placed at a distance of 20 cm from a converging lens of focal length 15 cm. The image obtained on the screen is : (a) upright and magnified (b) inverted and magnified (c) inverted and diminished (d) upright and diminished
(a) Explain with the help of a diagram, why the concave lens is also called a diverging lens. (b) Define the principal focus of a concave lens.
The diagram in Figure shows an object AB and a converging lens lens L with foci F1 and F2.
(a) Draw two rays from the object AB and complete the diagram to locate the position of image CD. Also mark on the Diagram the position of eye from where the image can be viewed.
(b) State three characteristics of the image in relation to the object.
Describe how you would determine the focal length of a converging lens, using a plane mirror and one pin. Draw a ray diagram to illustrate your answer.
(a) Explain why a real image can be projected on a screen but a virtual image cannot.
(b) Draw a ray diagram to show the formation of a real diminished image of an object by a convex lens. In your diagram, the position of the object and image with respect to the principal focus should be shown clearly.
(c) Name one simple optical instrument in which the above arrangement of the convex lens is used.
Focal length of convex lens is 20 cm, focal length of concave mirror is 30 cm. And the separation between lens and mirror is 90 cm. If the object is placed 60 cm before lens, find out position of image formed by concave mirror?
60 cm from point A
90 cm from point B
60 cm left of lens
60 cm from point B
Describe with the help of a ray-diagram, the size, nature and position of the image formed by a convex lens when an object is placed beyond 2f in front of the lens.
In ray diagrams why we always place objects above the principal axis
(a) Construct ray diagrams to illustrate the formation of a virtual image using (1) a converging lens, and (ii) a diverging lens. (b) What is the difference between the two images formed above ?